A dehumidifying element composed of a honeycomb structure with silica gel supported thereon has conventionally been produced by a process comprising immersing a honeycomb structure fabricated of inorganic fiber paper, such as glass paper and ceramic paper, in an aqueous alkali silicate solution, immersing the impregnated honeycomb structure in an aqueous solution of a water-soluble calcium salt or magnesium salt, followed by acid treatment (hereinafter called a first conventional process) or a process comprising repeating the steps of immersing the honeycomb structure in an aqueous alkali silicate solution and drying several times, immersing the impregnated honeycomb structure in an aqueous solution of a water-soluble calcium salt or magnesium salt, followed by acid treatment (hereinafter called a second conventional process).
Silica gel production by acid treatment of an alkali silicate is complicated and involves repetition of steps, and it has been desired to obtain silica gel through a single series of steps. According to the first conventional process, because the pick-up of the alkali silicate per single impregnation operation is limited, the above-described steps must be repeated until a sufficient amount of silica gel is built up for obtaining practical dehumidifying performance. The amount of silica gel produced could be increased by increasing the concentration of the alkali silicate solution. However, since an alkali silicate is highly viscous, the inorganic fiber paper would be clogged in a high concentration alkali silicate solution. Therefore, there is an upper limit of the alkali silicate concentration, and the steps should be repeated of necessity.
Where the second conventional process if followed, when an alkali silicate-impregnated honeycomb structure is again immersed in an alkali silicate aqueous solution, the previously supported alkali silicate partly dissolves in the immersing solution, resulting in poor production efficiency.
In the present situation, it is difficult to obtain a sufficient amount of silica gel for manifestation of practical dehumidifying performance through one series of steps.